A wide variety of gas sensor types are utilized to detect gases and other ambient air conditions. For example, electrochemical sensors are well known. Such sensors may include the use of a metal or plastic can, which houses a liquid electrolyte having electrodes immersed in the liquid. An opening or gas diffusion barrier allows atmosphere to ingress and make contact with a gas-sensing electrode. Infrared sensors are also well known. Infrared sensors advantageously utilize the characteristics of gases which show differing absorption spectrum at various infrared frequencies. Further, metal oxide based gas sensors, such as sensors employing precious metal (Pt, Pd, Au, Ag)-activated SnO2, are also known. Such sensors may utilize porous metal oxides which exhibit a shift in electrical parameters when exposed to differing gases. For example, such electrical parameters may include resistance and capacitance characteristics. Such metal oxide sensors may be housed in a metal and/or plastic cylindrical can or ceramic housing with an opening provided on one end of the can to allow ingress of gas through an active charcoal filter to contact a porous metal oxide bead that is positioned within the can. Often such metal oxide based sensors utilize high operation temperatures, for example as high as 300 to 500 degrees Celsius.
The use of metal oxide based gas sensor materials in combination with integrated circuit technology to provide an integrated gas sensor has been described in U.S. Pat. No. 7,554,134, issued Jun. 30, 2009 to Cummins, and U.S. Pat. No. 8,007,167, issued Aug. 30, 2011 to Cummins, both of which are assigned to the present assignee and the disclosures of both of which are expressly incorporated by reference herein in their entirety. As described in U.S. Pat. Nos. 7,554,134 and 8,007,167 a single chip wireless gas sensor may include metal oxide sensing materials combined with a microcontroller, wireless transmit/receive circuitry, and other electrical circuits, all on a single integrated circuit.